Feed cushioning mechanism



July 18,1944. I R. E. PRICE I 2,354,056

' I FEED CUSHIONING MECHANISM Fi led Dec. 8, 1941 2 Sheets-Sheet l l'mvcntor RALPH E. PB ICE 7%): M Gttomcg July 18, 1944. R, E PRICE 2,354,056

FEED CUSHIONING MECHANISM Filed Dec. 8, 1941 2 Sheets-Sheet 2 Inventor RALPH E; P12 105 Gttorncg Patented July 18, 1944 FEED CUSHIONING MECHANISM Ralph E. Price, Highfield, Md., assignor to Landis Tool Company, Waynesboro, Pa.

Application December 8, 1941, Serial No. 422,172

3 Claims.

This invention relates to feed mechanisms for metal working machines, and particularly to cushioning devices for such mechanisms.

In metal working machines, particularly grinding machines where a rapid feed movement is effected by a piston, and thru endwise movement of a feed screw and associated parts, such as a nut or the like, on the part being moved there is a certain amount of back lash between said parts. If the rapid movement is checked suddenly, the inertia of the sliding member will cause said member to continue at a rapid rate to a point depending upon the amount of back lash. Former attempts to solve this problem utilized a back lash piston connected to the sliding memher, but operating against pump pressure Furthermore, the back lash piston was under pump pressure at all times and any fluctuation in this pressure during feeding affected the performance of the feeding mechanism adversely.

The purpose of this invention is to remedy this condition by means of a piston and c linder, one of which is directly connected to the sliding member. Said cylinder is connected to the forward cushioning section of the power cylinder by means of a fluid passage. When fluid under pressure is directed to withdraw the sliding member to inoperative position, it acts also on the second piston which thus assists in the withdrawal move ment. When the slide is moved toward operative position, both cylinders are connected to the exhaust passage, in whi h a flow control valve determines the rate of exhaust, and, therefore, the rate of movement of the slide during the cushioned part of the stroke. The back pressure built up due to this restricted exhaust for cushioning is also effective against the second piston, which being connected directly to the sliding part, will counteract the effect of inertia on the slide and prevent said slide from jumping ahead of the driving side of the feed screw.

In the drawings, Figure 1 is an end elevation partly in section of a grinding machine wheel slide.

Figure 2 is a hydraulic diagram showing the method of applying my invention to a feed mechamsm.

Numeral indicates part of the bed of a grinding machine, I I a wheel support slidably mounted thereon, and I2 a grinding wheel rotatably mounted on said support. This wheel support ma be fed manually by a mechanism consisting of handwheel l3, shaft I4 having a worm gear (not shown) thereon, a worm wheel on vertical shaft l6, and a worm wheel I! on said vertical shaft engaging feed screw it. Said feed screw acts as a rack for worm wheel I 1.

Means for moving said wheel support I I by power consists of a rapid feed piston 2i] directly connected to screw [8. Said piston is mounted in cylinder 2| and supplies a rapid feed movement. When moved bodily endwise by piston 20, said screw being in engagement with worm wheel I! carries with it said worm wheel, the shaft IE on which it is mounted, and, therefore, the wheel support I l. A positive stop 25 in the path of said screw limits the rapid feed movement. The slow feed is effected by rotation of said screwin engagement withsaid worm wheel with the end of said screw in contact with said positive stop. The means for rotating said screw consists of a piston 30 and cylinder 3| positioned with the axis thereof perpendicular to that of said feed screw. Piston rod 32 has rack teeth 33 which engage a pinion 34 secured to the shaft of feed screw [8. Rotation of said screw causes Worm wheel I! to move relative thereto carrying support ll along with it.

A cylinder '40 formed in bed If] contains a piston 4|, one end of which is attached to wheel support II. A passage 45 connects the forward end of said cylinder with the forward end of cylinder 2| Fluid under pressure is supplied to the feed mechanism by a pump thru a line 5| to reversing valve 52. Said valve may be shifted manually by means of a knob 53 to direct fluid alternately to passages 55 and 5B.

T start the feeding movement the operator pulls knob 53 thus connecting line 5| with passage 56. Fluid in passage 56 flows thru check valve 51 and throttle valve 58 thru line 59 to the head end of cylinder 2 I. The function of throttle valve 58 is not to determine the rate of the rapid feed movement, as will be indicated later. Piston 20 moves to the right under the force of an unrestricted flow of fluid under pressure and exhaust fluid escapes unrestricted thru passage '55 and exhaust line '60. Fluid in passage 56 is also conducted thru passage to cylinder 3i to start the grinding feed portion of the feeding mechamsm.

As piston 20 moves forward it passes across the end of passage 55 thus cutting off the flow of exhaust fluid therethru. Exhaust fluid then flows thru line H! and throttle valve 15. Check valve 16 is closed to exhaust fluid. A pressure is built up in the exhaust fluid due to the throttle valve and the movement of piston 20. The rate of movement of said piston during this part of the stroke is determined by the setting of valve 15. The pressure thus built up is transmitted thru passage 45 to cylinder 40 and piston 4|. Since piston 4| is connected directly to the wheel support I l, and independently of piston 29, any tendency of the support to jump ahead upon the slow down of piston 20 due to inertia and lost motion or back lash is checked by the pressure against piston 4|. This pressure continues until screw l8 engages stop 25 at which time it becomes zero. The feeding movement which follows is thus free from the efiect of a fluctuating retarding pressure.

The combined area of piston 4i and piston 28 minus the screw i8 is substantially the same as that of the other end of piston 28. This permits the use of a greater volume of fluid and a larger orifice in the throttle valve for a given amount of cushioning. At the same time the added area of the piston 4| allows a lower operating pressure when the wheel support I l is moved in the opposite direction.

In order to move support i l in the opposite direction the operator pulls knob 53 and directs fluid under pressure thru passage 55. Said fluid enters the rod end of cylinder 3i to reset the grinding feed piston 30. Fluid also passes thru check valve 16 and line IE! to cylinders 2i and 49. Exhaust fluid from the head end of cylinder 25 escapes thru passage 56 until said passage is out off by piston 20. Thereafter, exhaust fluid must escape thru line 59 and throttle valve 58. Thus the rearward movement of the support i l is cushioned and a jarring stop prevented.

I claim:

1.. In a metal working machine, a movable slide, means for moving said slide including a piston and cylinder and hydraulic conneeticns therefor, means for resisting the operation of said moving means at a predetermined point in the movement of said slide including a throttle valve in the exhaust line, a back lash piston and cylinder one of which is connected directly to said slide and connections from said backlash cylinder to the exhaust passage of said slide moving means between said power cylinder and said throttle valve, the pressure built up against said throttle valve being effective to resist movement of said back lash piston.

2. In a metal working machine, a movable slide, means for moving said slide including a feed screw a piston and cylinder for eilecting longitudinal movement of aid screw and slide, longitudinally spaced exhaust passages in said cylinder one of said passages being free and the other having an adjustable restriction therein, a back lash mechanism consisting of a piston and cylinder one of which is connected to said slide independently of said slide moving means, said exhaust passages being connected also to said back lash cylinder, said free exhaust passage being so located that it is cut off by relative movement between said first mentioned piston and cylinder.

3. In a metal working machine, a movable slide, manually actuated means for moving said slide including a screw, power means operable through said screw for moving said slide including a piston and cylinder, a positive stop for determining the extent of movement of said screw and slide, means for checking the movement of said piston as the screw approaches the stop, and means for applying an opposing force directly against the slide only at the instant of checking, including a second piston and cylinder one of which is attached to said slide, a common exhaust system for said cylinders and means operable in response to movement of said first mentioned piston for throttling the flow of fluid thru said exhaust system.

RALPH E. PRICE. 

